In the process for catalytic conversion of olefins to heavier hydrocarbons by catalytic oligomerization using an acid crystalline zeolite, such as ZSM-5 type catalyst, process conditions can be varied to favor the formation of either gasoline or distillate range products. At moderate temperature and relatively high pressure, the conversion conditions favor distillate range product having a normal boiling point of at least 165.degree. C. (330.degree. F.). Lower olefinic feedstocks containing C.sub.2 -C.sub.6 alkenes may be converted selectively; however, the distillate mode conditions do not convert a major fraction of ethylene. While propene, butene-1 and others may be converted to the extent of 50 to 95% in the distillate mode, only about 10 to 20% of the ethylene component will be consumed.
In the gasoline mode, ethylene and the other lower olefins are catalytically oligomerized at higher temperature and moderate pressure. Under these conditions ethylene conversion rate is greatly increased and lower olefin oligomerization is nearly complete to produce an olefinic gasoline comprising hexene, heptene, octene and other C.sub.6.sup.+ hydrocarbons in good yield. To avoid excessive temperatures in the exothermic reactors, the lower olefinic feed may be diluted. In the distillate mode operation, olefinic gasoline may be recycled and further oligomerized, as disclosed in U.S. Pat. No. 4,211,640 (Garwood and Lee). In either mode, the diluent may contain light hydrocarbons, such as C.sub.3 -C.sub.4 alkanes, present in the feedstock and/or recycled from the debutanized product.